A vehicle drive system unit such as a transmission, a transaxle, and a driving power unit generally has a unit case fixed to and supported by a body-side supporting portion via a supporting member. The device described in Patent Document 1 is an example thereof and a driving power unit having an engine and a transmission is fixed to a mount device (body-side supporting portion) via a pair of brackets that are supporting members. Patent Document 1 also describes a technique of fastening these brackets with a stiffener for reinforcement (see paragraph 0005). Patent Document 2 describes a support structure of a transaxle, and a transaxle case thereof has multiple case members (a housing 14, a cylindrical case 16, and a cover 18) axially abutted against and bolt-fastened to each other and fixed to and supported by a mount device on the cover side. Patent Document 3 describes a technique of using a torque rod as a supporting member and providing a stiffener for reinforcing the torque rod.